Modeling Item‐Position Effects Within an IRT Framework

Changing the order of items between alternate test forms to prevent copying and to enhance test security is a common practice in achievement testing. However, these changes in item order may affect item and test characteristics. Several procedures have been proposed for studying these item‐order effects. The present study explores the use of descriptive and explanatory models from item response theory for detecting and modeling these effects in a one‐step procedure. The framework also allows for consideration of the impact of individual differences in position effect on item difficulty. A simulation was conducted to investigate the impact of a position effect on parameter recovery in a Rasch model. As an illustration, the framework was applied to a listening comprehension test for French as a foreign language and to data from the PISA 2006 assessment.